Water-soluble polymers can be prepared in several forms. For instance, it is known in the art that water-soluble polymers can be prepared in the dispersed phase of water-in-oil emulsions. This invention is directed to a new primary surfactant system for water-in-oil emulsions of water-soluble, ethylenically unsaturated polymers. More particularly, this invention relates to a process for producing polymer emulsions having greatly improved performance characteristics over other emulsions known in the art, while minimizing costs of manufacture. This invention is additionally directed to emulsions made using the process and surfactant system disclosed herein.
Water-in-oil emulsions are comprised of three components, including: (1) an aqueous phase; (2) a hydrophobic (oil) phase; and (3) a surfactant system. Through extensive research, the inventor has discovered that a surfactant system comprising an oil-soluble alkanolamide, polyoxyethylene derivatives of sorbitan esters and, optionally, sorbitan monooleate, can be used to produce water-in-oil emulsions of ethylenically unsaturated polymers which have the following unexpected characteristics: (1) improved settling storage stability; (2) small particle size; (3) low bulk viscosity; (4) improved high temperature tolerence; (5) low oil content; (6) improved solids loadings; and (7) comparable or improved performance without sacrifice of the above advantages.
U.S. Pat. No. 3,826,771 discloses the use of sorbitan monostearate and sorbitan monooleate as water-in-oil emulsifying agents. U.S. Pat. No. 3,278,506 further discloses the use of ethylene oxide condensates of fatty acid amides as emulsifiers. U.S. Pat. No. 3,284,393 suggests the use of hexadecyl sodium pthalate, sorbitan monooleate, sorbitan monostearate, cetyl or stearyl sodium pthalate and metal soaps as oil-in-water emulsifiers, while U.S. Pat. No. 4,024,097 discloses the use of surfactant systems comprising an oil-soluble alkanolamide, such as Witcamide 511, which is commercially available from Witco Chemical Company, and one or more co-emulsifiers selected from the group consisting of unesterified dialkanol fatty amide, quaternized ammonium salts of fatty tertiary amines, salts of fatty tertiary amines, alkaline metal salts of fatty acids and alkyl or alkylaryl sulfates or sulfonates.
The novel surfactant system described herein is not disclosed or suggested by the above-cited references. In fact, these references most commonly teach the use of so-called low hydrophilic-lipophilic balance (HLB) materials as emulsifying agents such as those having an HLB value of less than 5.0. In contrast, the surfactant system described herein is totally nonionic and requires the use of polyoxyethylene derivatives of sorbitan esters which commonly have HLB values in the range of 9.0 to 11.0.
Disadvantages are inherent in the use of many surfactant systems known in the art. For example, emulsions made with state of the art surfactant systems tend to separate over relatively short periods of time. This problem is closely related to the relatively large particle sizes which are common to presently-known emulsions. Also, high bulk viscosities keep active polymer concentrations low, and contemporary polymer emulsions lack high temperature tolerence. Generally, these difficulties cannot be remedied using known art without diminishing polymer performance. Finally, high oil concentrations of state of the art emulsions keep manufacturing costs high.
Accordingly, the need exists for a surfactant system which reduces oil requirements, and therefore manufacturing costs, improves settling storage stability, lowers emulsion bulk viscosity and improves solids loadings. It is thus an object of this invention to provide a novel surfactant system to the art comprising an oil-soluble alkanolamide, polyoxyethylene derivatives of sorbitan esters, and optionally, sorbitan monooleate, which accomplishes these objectives. It is a further object of this invention to provide to the art a process for the manufacture of water-in-oil emulsions which utilize the novel surfactant system of this invention. It is a still further object of this invention to provide water-in-oil emulsions of ethylenically unsaturated polymers having low oil contents, high solids loadings, improved settling storage stability, low bulk viscosities and low manufacturing costs, without sacrificing molecular weight.
Other objects of this invention will become apparent to those skilled in the art from the following detailed description.